The kidneys filter blood and remove wastes that are then transported through the ureters to the urinary_bladder. The bladder empties its contents through the urethra. The urethra of the male has a dual function. It carries urine as well as reproductive fluids (but not at the same time). The urethra of a female has only one function - urinary excretion. In humans, one adrenal_gland sits on top of each kidney; hence they are said to be suprarenal. In cats, however, the adrenals are separate from the kidneys and are embedded in mesentery.

The outer surface of the kidney is covered with a CT capsule, and has an indented region known as the hilus (hilum) where blood vessels and a ureter connect to the kidney.

The interior of the kidney is organized into two layers, the

(1) cortex and

(2) the medulla.

The cortical layer consists primarily of glomerular_capsules and the bulk of their associated tubules:

proximal_convoluted (PCT),

distal_convoluted (DCT), and

portions of the loop_of_Henle or nephron loop.

The medullary layer consists primarily of the extended portions of the Henle loops, and is organized into structures referred to as renal (or medullary) pyramids. Sections of cortical tissue (renal_columns) extend between these pyramids.

Below the medullary layer is the renal_pelvis, which leads to the ureter. The pelvis extends upward like a hand, and the "fingers" of the pelvis insert themselves between the medullary pyramids. These "fingers" are called the major_calyces (sing: major_calyx). The "tips" of the "fingers" are the minor_calyces (sing: minor_calyx).